1. Field of the Invention
The present invention relates to semi-trailer landing gear extension and retraction mechanisms, and more particularly to a landing gear mechanism that can be actuated by inexpensive, easily interchangeable pneumatic, hydraulic and electric motors as well as the traditional hand crank.
2. Description of the Prior Art
Many semi-trailers have front landing gear for support of the front of the trailer when the tractor is detached. Such landing gears generally have two spaced-apart, telescoping or Jack-type landing gear legs and feet which extend downwardly from the floor of the trailer. Each leg is operatively attached to screw and follower or a rack and pinion gear arrangement which is driven by a landing gear drive shaft which extends between the legs and which causes extension or retraction of the legs and feet depending on the direction in which it is rotated.
Traditionally, a hand operable handle or crank is attached to the landing gear drive shaft by a pin or bolt which serves as a hinge connection allowing the handle to be pivoted out of the way while not in use. Manual rotation of the handle in one direction causes extension of the feet and lifting of the trailer to, for example, separate the trailer from a semi-tractor, and requires considerable time and effort on the part of the person manually rotating the hand crank. Manually operated jack structures, however, are often difficult to use, require much time for their operation and expose the operator to potential injuries as he is positioned next to the trailer while turning the crank to raise or lower the landing gear to in turn raise or lower the trailer.
Thus, prior art attempts have been made to reduce the effort required to manually operate the crank handle. For example, a two-speed gear box, referred to as a gear reduction box, is typically included in the prior art landing gear to allow the hand crank handle to be attached to either a high speed or low speed input shaft of the gear box. The gear ratio utilized within the gear reduction box assembly depends upon the lateral positioning of the crank shaft and the outer diameter of the spur gears utilized in the gear box. In any event, the primary type of gear utilized in these gear boxes, as well as to transfer crank handle input power to the gear boxes, is the basic spur gear. While other types of gear configurations, such as worm gears, have been used in gear boxes, they have not been incorporated into the gearing of landing gear assemblies because of the need to incorporate gear reduction boxes within the assembly. To the extent a gear reduction box is included in a landing gear assembly, other types of gears, such as worm gears, are not utilized because they would simply distort or slow down the input speed of the crank handle. In other words, worm gears in combination with gear reduction boxes would reduce the effectiveness of the gear reduction boxes by altering the two speeds of the gear box.
Another attempt in the prior art to reduce operator input effort has been to retrofit existing landing gear with powered devices in order to raise and lower the landing gear. Generally, such retrofitted devices require an intricate system of spacers, pulleys and gearing that is both comparatively expensive and difficult to implement. This is especially true since the powered devices must be retrofitted to operate with gear reduction boxes. In any event, most of these powered devices have been pneumatically powered, although other power means have been used for the purpose. Typically, even beyond the general retrofit system, such pneumatic devices require a complex system to receive pressurized air for the actuators to rotate the crank shaft of the gear reduction assembly to raise and lower the landing gear. One class of prior art pneumatic devices has utilized pneumatic impact motors to drive the landing gear. Of course, those skilled in the art will understand that due to their pulsating drive mechanism, such pneumatic impact motors are not conducive to the desired smooth operation of raising and lowering the landing gear legs, especially in combination with gear reduction boxes. Another class of prior art pneumatic mechanisms dispenses with the gearing system of traditional landing gear and utilizes a pneumatic bladder to telescope the landing gear legs. Whichever type of pneumatic actuation system is used, however, such devices generally are permanently retrofitted as an integrated part of the reduction box and drive system of the landing gear.
Piston driven hydraulic devices are also known in the prior art. Similar to the pneumatic air bladder system referenced above, such devices replace traditional gearing systems and utilize hydraulic pistons to drive the landing gear. Once drawback to hydraulic pistons is that they do not provide the same positive holding as provided by a gearing arrangement. Power failure or loss of pressure could cause failure and collapse of the landing gear. In any event, such systems are generally large, cumbersome and permanently installed as an integrated part of the drive system.
Still yet other drive mechanisms have focused on the use of electric motors. The desirability of electric motors for powering landing gear is that they are generally easy to operate and require a less complicated motor control system. As with other types of motors, however, electric motors usually require specialized parts to link the motor to the gear mechanism and the motors are installed as an integral, permanent component of the landing gear system.
Because of the complexity and expense of prior art motor driven systems for raising and lowering landing gear, such systems have not been widely accepted in the trucking industry and old fashioned, hand crank systems still predominate in the field. Also because of the prior art's complexity and need for specialized parts, many of these motor driven systems have proven to be fragile and generally unsuitable to the rugged demands of long-haul semi-trailers in use on a daily basis.
Another drawback to the prior art is that manual operation of landing gear requires the operator to be in close proximity to the loaded trailer. As such, any shift in load or failure of the landing gear would put the operator in peril. Furthermore, in typical trailer arrangements, the operator must stand on the side of the trailer, near the front of the trailer, to operate the landing gear. In doing so, the operator may be exposed to traffic or other vehicles moving along side the trailer. This is especially dangerous for the operator when the trailer may be pulled off the road onto a road shoulder and the operator is forced to stand at the edge of the road to operate the crank handle. Finally, such manual operation subjects the operator to exposure to the weather, a prospect that can be unpleasant at best during rain, snow or hot weather and could exacerbate the other safety issues identified herein.
Each of the various types of prior art motor mechanisms for driving landing gear have there benefits and drawbacks. It would therefore be desirable to provide a motor driven landing gear system that takes advantage of each of the pneumatic, hydraulic and electric motor driven systems while avoiding the traditional drawbacks of these systems.